When I'm adding the suggested new repository from the following URL http://download.eclipse.org/eclipse/testUpdates/ I'm getting the
following exception (copied from the .log file):
org.eclipse.equinox.p2.core.ProvisionException: Unable to add repository http://download.eclipse.org/eclipse/testUpdates/
at
org.eclipse.equinox.p2.ui.operations.ProvisioningUtil.addMet adataRepository(ProvisioningUtil.java:46)
at
org.eclipse.equinox.p2.ui.operations.AddMetadataRepositoryOp eration.doExecute(AddMetadataRepositoryOperation.java:33)
at
org.eclipse.equinox.p2.ui.operations.UndoableProvisioningOpe ration.execute(UndoableProvisioningOperation.java:78)
at
org.eclipse.core.commands.operations.DefaultOperationHistory .execute(DefaultOperationHistory.java:511)
at
org.eclipse.equinox.p2.ui.ProvisioningOperationRunner$1.run( ProvisioningOperationRunner.java:50)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

There is indeed a lot of flux right now as we're leeding up to M5 with
slight changes in metadata here and there.
If you want to try an SDK install you can use the I20082006-0010 build as I
can confirm that works.